S8) Introduction to Neoplasia Flashcards
What is a neoplasm?
A neoplasm is an abnormal growth of cells that persists after the initial stimulus is removed
What are malignant neoplasms?
A malignant neoplasm is an abnormal growth of cells that persists after the initial stimulus is removed and invades surrounding tissue, potentially spreading to distant sites
What is a tumour?
A tumour is any clinically detectable lump or swelling
Describe the relationship between the following terms:
- Neoplasm
- Cancer
- Metastasis
- Neoplasm: one type of tumour
- Cancer: any malignant neoplasm
- A metastasis: a malignant neoplasm that has spread from its original site (primary site) to a new non-contiguous site (secondary site)
What is dysplasia?
- Dysplasia is a pre-neoplastic alteration in which cells show disordered tissue organisation
- It is not neoplastic because the change is reversible
Explain how benign and malignant neoplasms show different behaviour
- Benign neoplasms remain confined to their site of origin and do not produce metastases
- Malignant neoplasms have the potential to metastasise
Explain how benign and malignant neoplasms appear different to the naked eye
- Benign tumours grow in a confined local area and so have a pushing outer margin (rarely dangerous)
- Malignant tumours have an irregular outer margin and shape and may show areas of necrosis and ulceration, if on a surface
Describe the range of differentiation observed in malignant and benign neoplams respectively
- A benign neoplasm has cells that closely resemble the parent tissue, i.e. they are well differentiated
- Malignant neoplasms range from well to poorly differentiated
What are anaplastic cells?
Anaplastic cells are neoplastic cells with no resemblance to any tissue
Describe what happens to neoplastic cells with worsening differentiation
- Increases nuclear:cytoplasmic ratio
- Increased nuclear staining (hyperchromasia)
- More mitotic figures
- Increasing variation in size and shape of cells and nuclei (pleomorphism)
What is meant by the term grade?
Clinicians use the term grade to indicate differentiation e.g. high grade means poorly differentiated
Explain how dysplasia can describe different degrees of differentiation
- Dysplasia also represents altered differentiation
- Mild, moderate and severe dysplasia indicates worsening differentiation
What causes neoplasia?
Neoplasia is caused by accumulated mutations in somatic cells
Explain how mutations in neoplastic cells are caused by initiators and promoters
The mutations are caused by initiators (mutagenic agents) and promoters, which cause cell proliferation
What is the result of the combined efforts of intiators and promoters?
A combination of initiators and promoters results in an expanded, monoclonal population of mutant cells:
Describe the different types of initiators and/or sources of mutation in neoplastic cells
- Main initiatiors: chemicals, infections, radiation (some also act as promoters)
- In some neoplasms, mutations can be inherited rather than from an external mutagenic agent
What is progression?
Progression is the process through which a neoplasm emerges from its monoclonal population, characterised by the accumulation of yet more mutations
What are monoclonal cells?
Monoclonal cells are a collection of cells which all originate from a single founding cell e.g. blood cells
In four steps, explain how we know that neoplasms are monoclonal
⇒ An X-linked gene for the enzyme G6PD in tumour tissue from women has several alleles encoding different isoenzymes
⇒ In early female embryogenesis, one allele is randomly inactivated in each cell (lyonisation)
⇒ In heterozygous women, normal tissues will be patchwork of each type of isoenzyme (heat labile, heat stabile)
⇒ However, neoplastic tissues only express one isoenzyme (monoclonal)
Describe the genetic alterations which occur to proto-oncogenes and tumour suppressor genes
- Proto-oncogenes become abnormally activated (become oncogenes), favouring neoplasm formation
- Tumour suppressor genes, which normally suppress neoplasm formation, become inactivated
